Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$201.61	11.300%	$224.3919	$224.39	$224.40	$224.40
Purchase #2	$87.61	3.289%	$90.4915	$90.49	$90.50	$90.50
Purchase #3	$219.78	10.858%	$243.6437	$243.64	$243.65	$243.60
Purchase #4	$34.94	10.459%	$38.5944	$38.59	$38.60	$38.60
Purchase #5	$171.88	10.623%	$190.1388	$190.14	$190.15	$190.10
Purchase #6	$37.91	13.423%	$42.9987	$43.00	$43.00	$43.00
Purchase #7	$57.94	3.473%	$59.9523	$59.95	$59.95	$60.00
7 purchase totals =	$811.67		$890.2113	$890.20	$890.25	$890.20